I too wanted more power than the factory offered, and since I had to rebuild my engine from seized, I threw the check book at it. Your engine isn't too far off of mine, and I'm pushing around 406 at the crank. My recipe:
- Original 351 Cleveland 2V worked over by a local machine shop
- Balanced, Blueprinted, Magnafluxed
- Bored .060"
- 3-angle valve job, mild port & polish
- Edelbrock Performer intake
- Edelbrock 1406 Performer 600CFM carb
- Holley electric fuel pump
- CompCams High-Energy 270/270 @ .566" roller cam
- CompCams High-Energy lifters & pushrods
- CompCams High-Energy 1.73 roller rockers
- Crane Cams 7/16" screw-in rocker studs
- Keith Black 9.5:1 hypereutectic flat-top pistons
- Duraspark II ignition and distributor
- Accel Super-Coil & 8mm wires
- Hooker Competition ceramic-coated headers
- Pypes Street Pro mufflers
- Pypes 2.5" stainless exhaust with 'X' pipe
- Pypes 2.5" chrome 'slash' tips
The cam and 1.73 roller rockers made the most difference, but everything else contributed, with the 9.5:1 pistons helping immensely as well. I have 3.00 rear gears and have no issues getting a burn-out, while still enjoying cruising the freeway around 1800 rpm (with an AOD transmission, that is). I also have the factory 2V heads (which most probably think I'm weird not wanting 4V heads, but I'm quite happy with them).
As the others mentioned, what exactly does 'More Power' mean to you? There are no wrong answers, but depending on what you want the car to do, you might not even need to crack open the engine itself to get there. Maybe a rear gear change, if you have cruising gears like I do, can get you off the line a lot quicker if that's what you need (but kill your top end).
That entire list above ran me about $7K in 2012 money, BTW. A quick look on JEGS, and the cam kit, roller rockers, screw-in rocker studs, pistons, and Duraspark ignition system would probably run in that $2000-ish range, and with what you currently have, would probably get you in that 400HP range as well. Leave out the pistons, and you've saved around $400 and still increased horsepower by over 100 from the factory... and haven't pulled the main rotating mass from the engine. How deep into this are you willing to go?
Hope this helps.